Welcome from South Louisiana. I can't help you with the Juki. Hope you get an answer.
For me, strange noises usually mean my Brother jumped time and I have to take my machine to the shop. And, it won't sew at all. My long arm is an older Nolting. I've never had extra noises in the bobbin area. Just on the top side and it's usually because I don't have the it threaded correctly or the thread has slipped out of the tension discs. Sometimes, my bobbins aren't threaded evenly and will cause glitches. I know this is not really what you are talking about, so I know this probably won't help you.